The present invention relates to a laser control apparatus, more particularly, an apparatus which carries out power control of a semiconductor laser employed for an optical recording/reproducing apparatus, and can control the optical power stably even when an output light is modulated at high speed at the high-speed recording.
A semiconductor laser is generally employed as an optical pick up and the like in an optical recording/reproducing apparatus such as a CD player, a writable CD-R drive, an erasable CD-RW drive and the like. The power of a semiconductor laser varies greatly in accordance with a temperature change or changes with passage of time(lifetime), and therefore, it is necessary to carry out power control for stabilizing the power when employing a semiconductor laser as a light source in an apparatus for performing recording/reproduction into/from an optical recording medium such as an optical disk and the like.
Such prior art semiconductor laser power control apparatus is disclosed in Japanese Published Patent Application No. Hei. 1-204224 in detail.
FIG. 9 is a block diagram for illustrating a prior art semiconductor laser power control apparatus. In figure, numeral 10 denotes a semiconductor laser for radiating laser light to an optical disk; numeral 1 denotes a photodiode for receiving the irradiation light of the semiconductor laser 10; numeral 2 denotes a monitor circuit for monitoring the output of the photodiode 1; numeral 20 denotes a bottom hold circuit for holding a bottom level of the output from the monitor circuit 2; numeral 21 denotes a sample-hold circuit for sample-holding the output from the monitor circuit 2; numeral 22 denotes a peak hold circuit for holding a peak level of the output from the monitor circuit 2; numeral 19 denotes a control circuit for outputting a first, a second and a third digital signals corresponding to a bias reference voltage, an erase power reference voltage and a peak power reference voltage, respectively; numeral 26 denotes a D/A converter for converting the first digital signal outputted by the control circuit 19 to a bias reference voltage; numeral 27 denotes a D/A converter for converting the second digital signal outputted by the control circuit 19 to an erase reference voltage; numeral 28 denotes a D/A converter for converting the third digital signal outputted by the control circuit 19 to a peak power reference voltage; numeral 23 denotes a servo amplifier for comparing the bias reference voltage outputted by the D/A converter 26 with the bottom level which is held in the bottom hold circuit 20 to amplify the error; numeral 24 denotes a servo amplifier for comparing the erase reference voltage outputted by the D/A converter 27 with a sample-hold level which is held in the sample-hold circuit 21 to amplify the error; numeral 25 denotes a servo amplifier for comparing the peak power reference voltage outputted by the D/A converter 28 with the peak hold level which is held in the peak hold circuit 22 to amplify the error; numerals 7,8 and 9 denote current sources for generating the currents corresponding to the outputs of the servo amplifiers 23,24 and 25, respectively; numeral 11 denotes a switch means for disconnecting the current source 8 with the semiconductor laser 10 in accordance with data EFM1; numeral 12 denotes a switch means for disconnecting the current source 9 with the semiconductor laser 10 in accordance with data EFM2.
Next, the operation will be described. A portion of the output light from the semiconductor laser 10 is received by the photodiode 1 and the generated photoelectric current is converted to a voltage in the monitor circuit 2.
At reproduction from the optical disk, the reproduction power reference voltage VR which is outputted by the D/A (Read/Bias) converter 26 serving as a reference voltage source and a voltage which is obtained by the bottom hold circuit 20 by sample-holding the output of the monitor circuit 2 are compared by the servo amplifier 23 and a current is passed through the semiconductor laser 10 by the current source 7 which is controlled by the comparison result of servo amplifier 23 so that a reproduction power PR corresponding to the reproduction power reference voltage VR is constantly outputted.
At recording into an optical disk, as shown in FIG. 2, the power of the semiconductor laser 10 is modulated into the three values of bias power PB, erase power PE, and peak power PP, thereby recording is performed into the optical disk. Then, a portion of the output light from the semiconductor laser 10 is received by the photodiode 1, and a signal corresponding to the optical output is outputted from the monitor circuit 2. The signal from the monitor circuit 2 is held by the bottom hold circuit 20, the sample-hold circuit 21, and the peak hold circuit 22 respectively, and the bottom level, the erase level and the peak level of the optical output are detected respectively. Initially, the bias power PB can be obtained by switching the output of the D/A (Read/Bias) converter 26 serving as a reference voltage source in FIG. 9 to switch over from the VR to the bias power reference voltage VB corresponding to the bias power PB. The bias power reference voltage VB and the voltage which is held in the bottom hold circuit 20 are compared by the servo amplifier 23, and a current is passed through the semiconductor laser 10 by the current source 7 which is controlled by the comparison result of servo amplifier 23 so that the bias power PB corresponding to the bias power reference voltage VB is constantly outputted.
Next, the erase power PE is obtained by comparing the erase power reference voltage VE outputted by the D/A(Erase) converter 27 serving as a reference voltage source and the output from the sample-hold circuit 21 by the servo amplifier 24 and by passing an erase power current through the semiconductor laser 10 with the erase power current superposed on the bias power current by the current source 8 which is controlled by the comparison result of servo amplifier 24.
Further, the peak power PP is obtained by comparing the peak power reference voltage VP outputted by the D/A(Peak) converter 28 serving as a reference voltage source and the output from the peak hold circuit 22 by the servo amplifier 25 and by passing a peak power current through the semiconductor laser 10 with the peak power current further superposed on the erase power current by the current source 9 which is controlled by the comparison result of servo amplifier 25.
Meanwhile, the erase power PE and the peak power PP are turned on and off by the switch means 11 and 12 which are switched by data EFM1 and EFM2, respectively, and therefore the power of the semiconductor laser is modulated between the bias power PB, the erase power PE and the peak power PP. As shown in FIG. 3, the interval at which the modulation is performed between the bias power PB and the peak power PP is the interval at which pits are formed on the track, and when the switch means 11 and 12 are in the state of on and off, respectively, the intervals at which the value of the erase power PE is maintained are the intervals where the space between pits are erased and spaces are formed. The three power values (the value of the bias power PB, the value of the erase power PE, and the value of the peak power PP) can obtain the desired power values by changing the respective reference voltages of D/A converters 26, 27 and 28 serving as the reference voltage sources.
The conventional semiconductor laser power control apparatus is constructed as above, and it can perform such a control that the powers of peak and bottom of the semiconductor laser should be predetermined by detecting the powers of peak and bottom of the semiconductor laser.
By the way, in a CD-R drive, a CD-RW drive or the like, the recording of data into an optical disk is performed at high speed by such as so-called double-speed recording which performs recording of data at an average rotation speed which amounts to N times (N is an integer of 2 or above) of the reproduction rotation speed of a music CD player as a reference, thereby, it is necessary to increase the modulation speed of the laser to a higher one, and for controlling the laser power at such high-speed modulation, the conventional construction requires to detect the bias power PB, the erase power PE, and the peak power PP, respectively, and therefore a monitor circuit, a bottom hold circuit, and a peak hold circuit which can perform high-speed responses are required, thereby resulting in an increase in costs.
That is, even when the laser is modulated at high speed and the high speed modulated light is incident on a monitor photodiode, if a photodiode and a monitor circuit having low response speeds are used, delays or unsharpening of signals would be generated therein and unsharpening of a monitor output signal would also occur, and therefore, as shown in FIG. 3, the optical output waveform cannot be correctly reflected on the monitor output and even if an output signal of the monitor circuit has become of high speed, as the signal becomes of higher speed, the detection efficiency of the bottom hold circuit and the peak hold circuit are lowered, thereby making it difficult that the peak output level and the bias output level should be detected correctly. In addition, in order to avoid these problems, it is required for a monitor circuit, a bottom hold circuit, and a peak hold circuit to have the capability of high-speed response, thereby resulting in an increase in costs.
The present invention is made to solve the above-mentioned problems and has for its object to provide a laser control apparatus which can perform a stable power control even at a high-speed modulation even though employing a monitor photodiode and a monitor circuit which operate at a relatively low speed.
According to Claim 1 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical recording medium by a semiconductor laser, comprising: a reproduction power monitor means for monitoring an output of the semiconductor laser at reproduction just before recording; a bias power setting means for setting a bias power which is a minimum power outputted by the semiconductor laser at recording of pits into the optical recording medium, to a semiconductor laser driving means on the basis of a monitor value of the reproduction power monitor means; an erase power monitor means for monitoring an erase power which is a power outputted by the semiconductor laser at erasing between pits of the optical recording medium by sample-holding; an erase power setting means for setting the erase power to the semiconductor laser driving means on the basis of a monitor value of the erase power monitor means; and a peak power setting means for setting a peak power which is a maximum power outputted by the semiconductor laser at recording of pits into the optical disk to the semiconductor laser driving means, by operating a monitor value of the erase power monitor means.
According to Claim 1 of the present invention, the laser control apparatus is constructed as above, and therefore detects a power at reproduction just before recording and operates a bias power, and, as for an erase power, detects the power by a sample-hold and operates a peak power on the basis of the detected value of the erase power, and even if a low speed monitor photodiode and a low speed monitor circuit are employed, since the time when the erase power is being outputted is relatively long, the erase power can be correctly detected by the sample-hold and therefore the stable power control can be realized even at the high-speed modulation.
As described above, since the time when an erase power is being outputted is relatively long, the erase power can be detected correctly by a sample-hold, and by utilizing this, a laser control apparatus can realize the power control stably even at the high-speed modulation, even when a low speed monitor photodiode and a low speed monitor circuit are employed.
According to Claim 2 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical disk by a semiconductor laser, comprising: a photodiode for detecting a light of the semiconductor laser; a current/voltage conversion means for converting a current of the photodiode to a voltage and outputting the voltage; a reference voltage source for deciding a reproduction power of the semiconductor laser; an error detection means for detecting an error between the voltage outputted by the current/voltage conversion means and the reference voltage; a current source for passing a current through the semiconductor laser; a reproduction power control system for connecting an output of the error detection means to the current source, and controlling the reproduction power of the semiconductor laser; a bias current setting means for deciding a bias current to be passed through the semiconductor laser; a switch means for selectively switching between an output of the error detection means and an output of the bias current setting means, and at the reproduction, connecting an output of the error detection means to the current source to form the reproduction power control system and, at the recording, connecting an output of the bias current setting means, instead of the output of the error detection means, to the current source; a sample-hold means for sample-holding the output voltage of the current/voltage conversion means at the recording; an erase current setting means for deciding an erase current to be passed through the semiconductor laser; a peak current setting means for deciding a peak current to be passed through the semiconductor laser; and an operation means for operating set values of the erase current setting means and the peak current setting means on the basis of an output value of the sample-hold means.
According to Claim 2 of the present invention, the laser control apparatus is constructed as above, and therefore controls a bias power with using an automatic power control (Automatic Power Control; hereinafter, referred to as APC) value at reproduction just before recording, and, as for an erase power, detects the power by the sample-hold and subjects the power to APC directly, and controls a peak power on the basis of the control value of the erase power, and, even when a low speed monitor photodiode and a low speed monitor circuit are employed, since the time when the erase power is being outputted is relatively long, the erase power can be correctly detected by the sample-hold, and therefore the power control can be realized stably even at the high-speed modulation.
As described above, a bias power is controlled by using an APC control value at the reproduction just before recording, an erase power is controlled by the power being detected by the sample-hold, and a peak power is controlled on the basis of the control value of the erase power, and thereby a laser control apparatus which can realize power control stably even at the high-speed modulation can be provided even when a low speed monitor photodiode and a low speed monitor circuit are employed.
According to Claim 3 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical recording medium by a semiconductor laser, comprising: a semiconductor laser power monitor means for monitoring an output of the semiconductor laser; an output error detection means for detecting an error between an output power reference value which is to be outputted by the semiconductor laser at reproduction just before recording and an actual output power value at the reproduction, which value is detected by the semiconductor laser power monitor means; a semiconductor laser power control means for setting an output power target value to a semiconductor laser driving means on the basis of a detected result of the output error detection means; and an output power target value correction means for correcting the output power target value on the basis of a monitor value of an output of the semiconductor laser driving means after the output power target value is set.
According to Claim 3 of the present invention, the laser control apparatus is constructed as above. Thereby, it obtains an error between an actual output and an output reference value of a semiconductor laser when the state is changed from the reproduction state into the recording state, and sets, in accordance with the error, an output power target value to the semiconductor laser driving means, and monitors the output of the semiconductor laser driving means so as to correct the output power target value. Therefore, it is possible to set a bias power appropriately in accordance with a reproduction power as a reference.
As described above, the laser control apparatus which can appropriately set a bias power in accordance with a reproduction power as a reference can be obtained.
According to Claim 4 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical disk by a semiconductor laser, comprising: a photodiode for detecting a light of the semiconductor laser; a current/voltage conversion circuit for converting a current of the photodiode to a voltage, and outputting the voltage; a reference voltage source for deciding a reproduction power of the semiconductor laser; an error amplifier for amplifying a difference between the voltage outputted by the current/voltage conversion circuit and the reference voltage; a current source for passing a current through the semiconductor laser; a reproduction power control system for connecting an output of the error amplifier to the current source, to control the reproduction power; a D/A conversion circuit for deciding a current to be passed through the semiconductor laser; a switch means for selectively switching between an output of the error amplifier and an output of the D/A conversion circuit, to make a control signal of the current source; and an A/D conversion circuit for selecting one of an output voltage of the error amplifier and an output voltage of the D/A conversion circuit, and subjecting the voltages to digital conversion, in which a digital value of the D/A conversion circuit is decided on the basis of a digital value of the A/D conversion circuit, and at the recording, the output of the error amplifier is switched over to the output of the D/A conversion circuit and the current of the current source is controlled.
According to Claim 4 of the present invention, the laser control apparatus comprises: a reproduction power APC system for controlling the reproduction power to make the power constant at the reproduction; an A/D converter for detecting a current control voltage at reproduction; a D/A converter for controlling a bias current at the recording; a switch circuit for switching the control to switch over from a reproduction power APC system to D/A converter at the recording; and an operation circuit for operating the D/A value on the basis of the A/D conversion value, and makes a bias current value controlling a bias power equal to a reproduction current value controlling a reproduction power and can set the bias power to be equal to the reproduction power.
As described above, a laser control apparatus which can make a bias current value controlling a bias power equal to a reproduction current value controlling a reproduction power by detecting a reproduction current value and a bias power current value, and can set the bias power to be equal to the reproduction power, can be obtained.
According to Claim 5 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical disk by a semiconductor laser, comprising: a photodiode for detecting a light of the semiconductor laser; a current/voltage conversion circuit for converting a current of the photodiode to a voltage, and outputting the voltage; a reference voltage source for deciding a reproduction power of the semiconductor laser; an error amplifier for amplifying a difference between the output voltage of the current/voltage conversion circuit and the reference voltage; a current source for passing a current through the semiconductor laser; a D/A conversion circuit for deciding a current to be passed through the semiconductor laser; a switch means for selectively switching a control signal of the current source to switch between an output of the error amplifier and an output of the D/A conversion circuit; an A/D conversion circuit for subjecting an analog signal outputted from the current/voltage conversion circuit to digital conversion, and outputting the converted signal; and an operation circuit for, in a period during which recording is not performed, outputting a digital signal to the D/A conversion circuit, reading changes in the output signal of the A/D conversion circuit, obtaining a change amount in power in response to a change amount in the current of the semiconductor laser, and at the recording, outputting the digital signal value obtained above to the D/A conversion circuit.
According to Claim 5 of the present invention, the laser control apparatus comprises: a reproduction power APC system for controlling a reproduction power to make the power constant at the reproduction; an A/D converter for detecting a current control voltage at the reproduction; a D/A converter for controlling a bias current at the recording; a switch circuit for switching the control to switch over from the reproduction power APC system to the D/A converter at the recording; and an operation circuit for operating the D/A value on the basis of the A/D conversion value, and decides a bias current value to control a bias power with using a reproduction current value to control a reproduction power and can set the bias power freely.
As described above, a laser control apparatus which can obtain a bias power corresponding to a bias power current value previously, and can set the bias power freely, can be provided.
According to Claim 6 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical disk by a semiconductor laser, comprising: a photodiode for detecting a light of the semiconductor laser; a current/voltage conversion circuit for converting a current of the photodiode into a voltage, and outputting the voltage; a reference voltage source for deciding a reproduction power of the semiconductor laser; an error amplifier for amplifying a difference between the output voltage of the current/voltage conversion circuit and the reference voltage; a current source for passing a current through the semiconductor laser; a reproduction power control system for connecting an output of the error amplifier to the current source, and controlling the reproduction power; a D/A conversion circuit for deciding a current to be passed through the semiconductor laser; a switch means for selectively switching between the output of the error amplifier and an output of the D/A conversion circuit, to make a control signal of the current source; an A/D conversion circuit for subjecting the output of the error amplifier to digital conversion; and an operation circuit for, in a period during which recording is not performed, outputting a digital signal to the D/A conversion circuit, reading changes in an output signal of the A/D conversion circuit, obtaining a change amount in power in respect to a change amount in the current of the semiconductor laser, and at the recording, outputting a digital signal value obtained in the period during which the recording is not performed, to the D/A conversion circuit.
According to Claim 6 of the present invention, the laser control apparatus takes a correction between an A/D converter detecting a current control voltage at the reproduction and a D/A converter controlling a bias current at the recording, and even when full scales are different or offsets are present between the A/D converter and the D/A converter, the bias power can be set highly precisely.
As described above, a laser control apparatus which, by taking a correction between an A/D converter detecting a current control voltage at the reproduction and a D/A converter controlling a bias current at the recording, can set a bias power highly precisely even when full scales are different or offset are present between the A/D converter and the D/A converter, can be provided.
According to claim 7 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical recording medium by a semiconductor laser, comprising: a semiconductor laser power monitor means for monitoring an output of the semiconductor laser; an output error detection means for detecting an error between an output power reference value to be outputted by the semiconductor laser at reproduction just before recording and an actual output power value at the reproduction, which value is detected by the semiconductor laser power monitor means; a semiconductor laser power control means for setting an output power target value to a semiconductor laser driving means on the basis of the detected result of the output error detection means; a switch means for making a state between the semiconductor laser power monitor means and the output error detection means OFF at the recording, and making the state ON at the reproduction; and an output error setting means for setting the output of the output error detection means so as to be equal to the output power reference value at the recording.
According to Claim 7 of the present invention, the laser control apparatus is constructed as above. Thereby, it obtains an error between an actual output and an output reference value of the semiconductor laser when the state is changed from the reproduction state into the recording state, and, when an output power target value is set to the semiconductor laser driving means in accordance with the error, it sets the output error to be equal to the output power reference value without transmitting the monitor result of the semiconductor laser power monitor means to the output error detection means at the recording. Therefore, it is possible to avoid a transient response at switching from the recording state to the reproduction state.
As described above, a laser control apparatus which can avoid transient response when the state is switched from the recording state to the reproduction state, can be obtained.
According to Claim 8 of the present invention, there is provided a laser control apparatus which controls a power of a semiconductor laser in an optical recording/reproducing apparatus for performing recording/reproduction into/from an optical disk by a semiconductor laser, comprising: a photodiode for detecting a light of the semiconductor laser; a current/voltage conversion circuit for converting a current of the photodiode to a voltage, and outputting the voltage; a reference voltage source for deciding a reproduction power of the semiconductor laser; an error amplifier for amplifying a difference between the output voltage of the current/voltage conversion circuit and the reference voltage; a current source for passing a current through the semiconductor laser; a reproduction power control system for connecting an output of the error amplifier to the current source, and controlling the reproduction power; a D/A conversion circuit for deciding a current to be passed through the semiconductor laser; a switch means for selectively switching a control signal of the current source to switch between the output of the error amplifier and an output of the D/A conversion circuit; and a switch means for cutting off an input from the current/voltage conversion circuit into the error amplifier, in which at the recording, switching from the output of the error amplifier to the output of the D/A conversion circuit is performed to control the current of the current source, as well as the input from the current/voltage conversion circuit into the error amplifier is cut off, and at the reproduction, switching from the output of the D/A conversion circuit to the output of the error amplifier is performed to control the current of the current source, as well as the output of the current/voltage conversion circuit is connected to the input to the error amplifier, and the voltages of the reference voltage source, which decide the reproduction power, have different values at the recording and at the reproduction and, when switching from recording to reproduction is performed, the voltage of the reference voltage source is changed passing through at least one intermediate value.
According to Claim 8 of the present invention, a laser control apparatus which, being provided with a means for cutting off an input to a servo amplifier from a monitor circuit at the recording, and a means which can change a reference voltage of reproduction APC at switching from the recording state to the reproducing state, changes the reference voltage of the reproduction APC successively when the recording is switched to the reproducing, thereby to avoid the occurrence of an unusual output light according to transient response of the reproduction APC.
As described above, a laser control apparatus which, when the recording is switched to the reproducing, can change a reference voltage of reproduction APC successively, thereby to avoid the occurrence of an unusual output light according to transient response of the reproduction APC, can be provided.